This invention relates to devices for sensing the current in wires, particularly to devices for attachment to a pair of wires without having to disconnect or break the wires for sensing the current in the wires.
It is often desirable to be able to measure the current flowing through a circuit without a direct electric connection to the circuit through which the current flows. One way of doing this is to employ a Hall effect device as a magnetic field strength-to-voltage transducer. Since the current in a wire produces a magnetic field around the wire, the magnitude of the current in the wire can be determined by measuring the strength of that magnetic field. As is commonly known in the art, the voltage output of a linear Hall effect device is proportional to the strength of the magnetic field passing through it. So, where a linear Hall effect device is placed adjacent a wire so that the magnetic field produced by current in the wire passes through the Hall effect device, the voltage output of the Hall effect device is proportional to the current in the wire.
In the prior art, Hall effect devices used for current measurement are sometimes mounted in an essentially monolithic assembly having an aperture through which a wire is fed. This requires that the assembly be installed prior to conecting the wire in its circuit, or that the wire be disconnected so that the assembly can be installed. Often that is inconvenient, as in the case of an existing circuit such as a starter current circuit for a vehicle, which requires heavy duty cable to carry a large amount of current and is therefore difficult to disconnect and reconnect. While there is at least one prior art assembly for holding a Hall effect device adjacent a wire which employs a metal loop that wraps around the wire and a Hall effect device sandwiched between the ends of the loop, installation of such a device on a heavy-duty cable requires bending and concomitant distortion of the loop which not only is awkward and difficult to accomplish, but may decrease the effectiveness of the device.
Prior art devices also often include current concentration elements. These are typically a piece of magnetic material mounted adjacent the transducer to increase the flux density of the magnetic field in the transducer, i.e., to "focus" the magnetic field in the transducer. Some prior art assemblies include a nearly complete magnetic circuit around the wire to guide the magnetic field into the transducer, such as a torroid of magnetic material with a transducer disposed in a gap in the torroid. Such prior art flux concentration elements are fixed in their relationship with the transducer so that the sensitivity of the assembly is fixed. The fixed sensitivity of such assemblies limits their range of applicability.
Thence, it can be seen that there is a need for a current sensor assembly that can be conveniently installed in an existing electric circuit without a direct electrical connection, and which provides sensitivity adjustment.